ControllerInterface: devices population is now async so implement devices sorting priority

This helps us keeping the most important devices (e.g. Mouse and Keyboard) on the top
of the list of devices (they still are on all OSes supported by dolphin
and to make hotplug devices like DSU appear at the bottom.

Source/Core/InputCommon/ControllerInterface/DInput/DInputKeyboardMouse.cpp

@@ -230,6 +230,12 @@ std::string KeyboardMouse::GetSource() const
   return DINPUT_SOURCE_NAME;
 }
 
+// Give this device a higher priority to make sure it shows first
+int KeyboardMouse::GetSortPriority() const
+{
+  return 5;
+}
+
 // names
 std::string KeyboardMouse::Key::GetName() const
 {